Discharge devices for generating streamer discharges are known in the conventional art. One such discharge device is made up of a needle-like discharge electrode having a pointed tip and a sheet-like counter electrode (see for example JP, 2002-361028, A). In the discharge device of this patent gazette, the discharge electrode is positioned so as to be oriented perpendicularly to the surface of the counter electrode, with its tip positioned to lie adjacent to the counter electrode. The discharge device is configured, such that it generates a streamer discharge from the tip of the discharge electrode towards the counter electrode by application of discharge voltages to both the electrodes.
In the above-described discharge device, a low-temperature plasma is generated by streamer discharge. The low-temperature plasma contains substances of high reactivity (i.e., activated species such as electron, ion, ozone, and radical). And, such a type of discharge device is employed for example in air purifying devices which use a high-reactivity substance contained in a low-temperature plasma for decomposing and removing harmful substances and odorous substances in the air.
Problems that the Invention Intends to Solve
In a conventional discharge device, however, the tip of a discharge electrode wears by small degrees because of the effect of high-speed electrons and activated species which are generated during the discharge. As a result, the tip of the discharge electrode changes shape with time. And, when the tip of the pointed, needle-shaped discharge electrode becomes worn out, the diameter of the tip becomes somewhat increased. As a result, the distance between the discharge electrode and the counter electrode widens. Consequently, the discharge characteristic changes, and the streamer discharge becomes unstable. In addition, if voltages of higher level are applied with a view to coping with the increase in the distance between the discharge electrode and the counter electrode, this tends to arise problems such as spark generation.
With these problems in mind, the present invention was made. Accordingly, an object of the present invention is to prevent, in a discharge device which generates a streamer discharge from the tip of a discharge electrode towards a counter electrode, the streamer discharge stability from deteriorating even when the tip of the discharge electrode (41) becomes worn out.